In recent years, thermal transfer systems have been developed to obtain prints from pictures which have been generated electronically from a color video camera. According to one way of obtaining such prints, an electronic picture is first subjected to color separation by color filters. The respective color-separated images are then converted into electrical signals. These signals are then operated on to produce cyan, magenta and yellow electrical signals. These signals are then transmitted to a thermal printer. To obtain the print, a cyan, magenta or yellow dye-donor element is placed face-to-face with a dye-receiving element. The two are then inserted between a thermal printing head and a platen roller. A line-type thermal printing head is used to apply heat from the back of the dye-donor sheet. The thermal printing head has many heating elements and is heated up sequentially in response to the cyan, magenta and yellow signals. The process is then repeated for the other two colors. A color hard copy is thus obtained which corresponds to the original picture viewed on a screen. Further details of this process and an apparatus for carrying it out are contained in Brownstein U.S. Pat. No. 4,621,271 entitled "Apparatus and Method For Controlling A Thermal Printer Apparatus," issued Nov. 4,1986, the disclosure of which is hereby incorporated by reference.
Dye-receiving elements used in thermal dye transfer generally comprise a polymeric dye image-receiving layer coated on a support. A compression, or cushion intermediate layer, for example as taught by Harrison et al. in U.S. Pat. No. 4,734,397, may also be present between the support and the dye image-receiving layer. Such cushion layers promote better contact between a dye-donor element and the dye image-receiving element, which minimizes the formation of image defects during dye transfer and improves the scratch resistance of the receiving element. Further, subbing layers, for example as taught by Vanier et al. in U.S. Pat. No. 4,748,150, may also be present between the various layers in order to promote adhesion.
When a cushion layer is used between the receiver support and dye image receiving layer, and a subbing layer is also used between the cushion layer and the dye image-receiving layer, it is highly desirable to be able to coat the cushion and subbing layers simultaneously in one operation from miscible ketone based solvents rather than in a multiple coating-drying-coating-drying cycle in order to most efficiently manufacture the receiving element. It has been found, however, that simultaneous coating of cushion layers such as polyalkylacrylate esters and subbing layers such as vinylidene chlorides and polyvinyl acetate results in severe layer thickness nonuniformities in the coated layers due to formation of crater shaped repellancy spots, even when using miscible coating solvents such as butanone and acetone. Further, while the use of surfactants which lower the surface tension of such ketone solvents would be expected to facilitate coating, use of many of such known surfactants were found to still result in unacceptable coatings.
As such, it would be desirable to provide a manufacturing process which would enable the simultaneous coating of cushion layers and subbing layers on a support for a thermal dye transfer receiving element without a significant level of nonuniformities in the resulting coated layers.